What distro will use less resources for a laptop?

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http://unix.stackexchange.com – Currently I'm in doubt: I'm getting a new Dell Vostro 2520 with 4 gigs of memory. The problem is that I'm Ruby/ ex-php developer and may have to work with quite big projects. probably simultaneously. One option is upgrading a memory up, but i prefer the idea of getting to know available linux distributions and selecting a more suitable one. In the end there are two linuxes on my list: Linux mint Xfce Xubuntu What can you advice? (HowTos)